This dissertation is a philosophically constructive treatment of the modal ontological argument. Formulated by St. Anselm in the eleventh century, the ontological argument was almost immediately subject to criticism, and the intervening years have seen refinements of both the argument and its critiques. The twentieth century saw a renewal of interest in the argument on the part of thinkers such as Charles Hartshorne, who formulated the argument in terms of modal logic. Hartshorne further worked to elucidate the connection between the success of the argument and a coherent metaphysical account of God. My work engages the neoclassical metaphysics of Charles Hartshorne and Alfred North Whitehead with recent work by analytic philosophers of religion including Alvin Plantinga and Peter van Inwagen.,The major aim of the project is a formulation and defense of a modal ontological argument. I begin with a discussion of the force of arguments generally, regarding what we can and cannot expect them to accomplish. I examine the ontological argument in terms of these expectations, and show that the argument’s critics, and some of its proponents, misinterpret a major portion of Anselm’s original version of the argument. To this, I offer a revised reading of Anselm, according to which the second and third chapters of the Proslogion present two successive steps required for a valid argument, rather than two distinct arguments or two versions of the same argument. ,Through clarification of this presentation, I show that the familiar set of parodies of the argument are not relevant to its proper formulation, and thus do not hold sway against it. Next, I defend the argument in terms of its logical structure, arguing that the modal logic required for a valid ontological argument is reasonable to accept, despite potential objections. I then proceed to a discussion of the premises of the argument in terms of metaphysical necessity and possibility. I maintain that the premises of the argument are reasonable to accept on the basis that (a) metaphysical necessity is a logically coherent concept, and (b) there is a means to argue from what is and is not conceivable to the possibility of a necessary existent. My defense of the ontological argument serves the second important function of suggesting ways that the neoclassical metaphysics of Hartshorne and Whitehead should be attractive to those interested in endorsing modal ontological arguments. I conclude with an overview of some implications of adopting a neoclassical position.